Pickup



March 19, 1946. B. R. KAMLER ET AL PICK-UP Filed July 21, 1943 Patented Mar. 19, 1946 PICKUP Ben R. Kamler, Chicago, and David L. Elam,

Roselle, Ill., assignors to Alfred Crossley Application July 21, 1943, Serial No. 495,610

6 Claims.

This invention relates to a pick-up, and more particularly to a pick-up for translating the explosion or detonation pressure variations in an internal combustion engine into corresponding electrical variations.

One feature of this invention is that it is particularly adapted to give an indication of the rate of pressure variation within an internal combustion engine during its operation, so that differences in fuels and other factors may be tested; another feature of this invention is that it provides a considerably increased electrical output, as compared with prior pick-ups, per unit of pressure variation; still another feature is the provision of a novel means of adjusting sensitivity and locking the parts together without losing said sensitivity adjustment; yet another feature oi this invention is that it achieves a very high degree of magnetic efiiciency with a rela tively small permanent magnet; other features and advantages of this invention will be apparent from the following specification and the drawing, in which:

Figure l is a side elevational view of a device embodying our invention; Figure 2 is a vertical sectional view of such device, along the line 22 of Figure 1; Figure 3 is a top plan view of the device; and Figure 4 is a transverse sectional view along the line 4--4 of Figure 2. a

In connection with test work associated with internal combustion engines, and particularly determination of detonation characteristics of fuels, pressure variations in the engine provide an indication which is studied. While the pressure variations may be studied in any conventional internal combustion engine, as an automobile, aircraft or Diesel engine, such work is generally done in a one-cylinder engine especially designed for test work and known as a CFR (Consolidated Fuel Research) engine.

Electrical indication of pressure variations in such an engine has heretofore been most commonly provided by what has been known as a bouncing pin pick-up, operating by opening and closing contacts. Such a pick-up has many objections. More recently efforts have been made to get the desired electrical variations by a pickup on the piezo-electric or magnetic principles, and the present invention is directed to an im proved pick-up of the latter type.

The assignee of this application is now marketing a complete improved system for indicating detonation characteristics. This includes not only the pick-up here disclosed and claimed, but

also improved electrical circuits comprising the subject matter of other copending .applications.

The detonation or knock" frequencies which are of particular interest are a function of the cubical content of the cylinder at the time of the detonation, and usually range between 2,000 cycles per second (in large Diesel engines) and ten or twenty thousand cycles per second (in very small, high speed engines). Applicants sys' tem employs the pick-up which is the subject'of this application, passes the electrical variations derived from it through a tuned filter or other arrangement which separates the knock frequency from other undesired frequency variations present in the current, then passes the output of the filter through an amlifier and secures the desired indication from an oscilloscope or a special circuit which applicants have developed to actuate a milliammeter calibrated as a knock meter. In the CFR engine, for example, the knock frequency is usually very close to 6500 cycles per second, and the filter is tuned to this frequency and is arranged to pass a band width sumcient to enable indication of all the detonation frequencies at a particular speed of the test engine.

Referring now more especially to the particular embodiment of the invention illustrated herewith, the pick-up is shown as comprising, along with the other elements of the combination to be hereafter described, a cast cylindrical slug of aluminum nickel steel alloy, highly magnetized to provide a very powerful permanent magnet, this magnet being here identified as ill. The magnet is slipped into and loosely received within a cup-dike member ll of non-magnetic material, preferably of non-magnetic metal such as brass. This cup-like member is entirely open at the top, and is provided with a small opening or hole l2 in the bottom and is slotted on one side to prevent short circuited turn effect.

A headed rod member l3 of material of high magnetic permeability, as cold rolled steel, has a shank portion |3a received within the opening l2, and an enlarged head portion |3b adapted to lie within the cup-like member.

A coil 14 is wound around the shank of the 7 rod member, this coil preferably comprising a, large number of turns of fine wire with a very high heat resistant insulation, as glass insulation, the coil being subsequently protected by an overlying layer of ceramic or plastic material IS.

The cup-like member II is a force fit in a pocket within an upper holding member I6. In assembling the parts, the rod member is slipped through the opening l2 from the inside of the cup-like member I I, then the permanent magnet I is slipped down in and the cup-like member I I forced up into the pocket in the holding member I6 to hold the parts in the desired relationship, as illustrated in Figure 2. When the parts have been thus assembled the magnet cylinder I0 is firmly clamped in place by engagement with its two end surfaces.

The member I6 is threaded, for assembly and adjustment, into an adapter or outer shell H, the two being maintained in desired operative rela= tionship by locking means. This means is here shown as comprising set screws ida and 58b threaded into an annular 'fiange ltd on the hold ing member it, this arrangement providing locking means which does not interfere with the use of a socket wrench on the shell. A spring washer 24, which may be of phosphor bronze, keeps slack. out of the interengaging screw threads to avoid disturbance of the adjustment by operation of the set screws in. One side of the cup-like member H has a slot milled therein, the wire Mid extending through this slot and terminating in a central connector element [I9 in a connector plug 20 carried in the top of the holding member it.

The adapter or outer shell it may be described as generally cylindrical, although actually it is polygonal in shape (usually hexagonal) to enable its lower threaded portion lid to be firmly seated in a threaded hole in the engine being tested by the use of a socket wrench. It will be understood, of course, that this hole must be in addition to the hole for the spark plug which is firing the engine during testing. This shell surrounds but is spaced from the magnet ill, cup-like member ii, rod member 62 and coil id; and, near its lower end, provides a mounting for a diaphragm member 2i. This is a small spring steel dia= phragm, generally with a thiclmess between fifteen and thirty thousandths of an inch, and the end of the cooperating holding portions are lapped to make a perfect seal under the pressures encountered in an internal combustion engine. This diaphragm is held in place, of course, by the insert 22 threaded into the lower end of the adapter shell.

As may be best seen in Figure 2, the cylin= drical permanent magnet slug id, the rod mem-'- ber 53, the coil i l, and the shell il are coaxial; and the diaphragm 2i is in a plane perpendicular to such axis, with its movable center closely adjacent but slightly spaced from the lower end of the rod member iii. The rod member is lrept properly centered within the shell, at its lower end, by a spacer of non-magnetic material, as the slit-brass washer In placing the pick-up in the engine, the combination is inserted in the hole in the engine and the shell screwed tightly into the hole, as by use of a socket wrench. The other parts are then threaded down into the shell until the lower end of the rod member touches the diaphragm whereupon, the holding member is is backed off about A. turn (where the threads are 27 to the inch) to provide a space of about twelve thousandths of an inch between the end of the rod member and the diaphragm; and then the parts are locked in the desired relationship by the set screws it. In order to get the desired magnetic efllciency, this space between the lower end of the rod member and the diaphragm should be quite small, preferably between 10 and 20 thousandths of an inch.

The holding member it, the shell Hi, and the diaphragm 2| are all of material of high mag net IO, one pole of this magnet, abuts directly against a part of the holding member [6, and

i the lower end or other pole of the magnet abuts directly against the head of the rod member l3, so that a magnetic flux path is provided'from the lower pole through the rod member (threading the coil) across the air gap to the diaphragm and back to the other pole through the shell and holding member iii. Variation in the spacing of the air gap, by the effect of pressure against the lower side of the diaphragm 2i, varies the number of lines of flux threading the coil and thus creates a voltage difierential in the coil which is a function of pressure variations in the engine. The starting turn of the coil is grounded directly to the rod member and thus to the shell of the device and the engine; and the end turn of the coil is connected (by a shielded cable making connection to the connector plug at the top) to the filter, amplifier and indicating arrangement. The shield of the cable connects the grounded pick-up terminal to the ground terminal on the filter.

It is of particular importance from the standpoint of efiiciency that the upper end of the permanent magnet abuts directly against material of high magnetic permeability; and yet that the sides of the magnet cylinder, and particularly the lower end or pole face, be considerably spaced from the outer shell, to avoid magnetic flux leakage and short circuiting. The space between the bottom end of the magnet i ii and the inner walls or sides of the shell ill should be at least five and preferably ten or more times the space between the rod member and diaphragm, so that the de-- sired flux path will have a very much lower reluctance than a leakage path directly from the lower pole of the magnet to the shell.

Moreover, a pick-up of this type is subjected to terrific vibration, to very considerable heat during normal operation and to excessive heat when a diaphragm ruptures, as occasionally hap= pens. It is for this reason that the coil is preferably covered with a ceramic or plastic protective coating; and that proper spacing of the magnet from the sides of the shell presents a real problem. This problem has been solved here by the use of the cup-like member ii, and this member is a highly important factor in the combination. To lessen the effect of heat during normal operation, the shell is provided with holes s i'lb, lid, etc.; and an air hose or similar means may be used to force air through these holes during test operation.

While we have shown and described certain embodiments of our invention, it is to be understood that it is capable of many modifications. Changes, therefore, in the construction and arrangement may be made without departing from the spirit and scope of the invention as disclose in the appended claims.

We claim:

1. A pick-up of the character described for translating detonation pressure variations into corresponding electrical variations, including: a permanent magnet comprising a cylindrical slug; 3. cup-like member of non-magnetic material snugly receiving said magnet, this member having an opening in the bottom thereof; a coil; a rod member of high magnetic permeability extending through said coil and opening and having one end abutting one pole of said magnet with the rod member being of smaller diameter than said magnet; a flexible diaphragm member of high magnetic permeability, the plane of this member being transverse to the axis of the rod member and the center of the, diaphragm being adjacent but slightly spaced from the other end of the rod member; a substantially cylindrical shell of high magnetic permeability having the diaphragm member mounted in one end thereof and providing a housing for the magnet, cup-like member, coil and rod member and a member of high magnetic permeability mounted in the other end of the shell and abutting the other pole of the magnet, whereby substantially all of the magnetic flux between the poles is concentrated in a path through allof said members and the space between the diaphragni and rod members.

2. A pick-up of the character described for translating detonation pressure variations into corresponding electrical variations, including: a permanent magnet comprising a cylindrical slug; a cup-like member of non-magnetic material snugly receiving said magnet, this member havthe other end of the rod member; a substantially cylindrical shell of high magnetic permeability having the diaphragm member mounted in one end thereof and providing a housing for the magnet, cup-like member, coil and rod member; and a member of high magnetic permeability mounted in the other end of the shell and abutting the other pole of the magnet, whereby substantially all of the magnetic flux between the poles is concentrated in a path through all of said members and the space between the diaphragm and rod members.

3. A pick-up of the character described for translating detonation pressure variations into corresponding electrical variations, including: a permanent magnet comprising a cylindrical slug; a cup-like member of non-magnetic material snugly receiving said magnet, this member having an opening in the bottom thereof; a coil; a rod member of high magnetic permeability extending through said coil and opening and having one end abutting one pole of said magnet; a flexible diaphragm member of high magnetic permeability,

iii

the plane of this member being transverse to the axis of the rod member and the center of the diathe other end of the rod member; a substantially cylindrical shell of high magnetic permeability having the diaphragm member mounted in one end thereof and providing a housing for the magnet, cup-like member, coil and rod member; and a member of high magnetic permeability mounted in the other end of the shell and abutting the other pole of the magnet, the upper end of said cup-like member being mounted in said lastmentioned member, whereby substantially all of the magnetic flux between the poles is concentrated in a path through all of said members and the space between the diaphragm and rod members.

4. A pick-up of the character described for translating detonation pressure variations into corresponding electrical variations, including: a permanent magnet comprising a cylindrical slug; a cup-like member of non-magnetic material snugly receiving said magnet, this member having an opening in the bottom thereof; a coil; a rod member of high magnetic permeability extending through said coil and opening and having one end abutting one pole of said magnet; a flexible diaphragm member of high magnetic permeability, the plane of this member being transverse to the axis of the rod member and the center of the diaphragm being adjacent but slightly spaced from the other end of the rod member, the walls of the cup-like member being at least three times as thick as the space between the diaphragm and rod members, one side of said Wall being slotted to eliminate short circuited turn effect; a substantially cylindrical shell of high magnetic permeability having the diaphragm member mounted in one end thereof and providing a housing for the magnet, cup-like member, coil and rod member; and a member of high magnetic permeability mounted in the other end of the shell and abutting the other pole of the magnet, whereby substantially all of the magnetic flux between the poles is concentrated in a path through all of said members and the space between the diaphragm and rod members.

5. A pick-up of the character described for translating detonation pressure variations into corresponding electrical variations, including: a permanent magnet comprising a cylindrical slug; a cup-like member of non-magnetic material snugly receiving said magnet, this member having an opening in the bottom thereof ;a coil; 2. rod member of high magnetic permeability extending through said coil and opening and having one end abutting one pole of said magnet with the rod member being of smaller diameter than said magnet; a flexible diaphragm member of high magnetic permeability, the plane of this member being transverse to the axis of the rod member and the center of the diaphragm being adjacent but slightly spaced from the other end of'the rod member; a substantially cylindrical shell of high magnetic permeability having the diaphragm member mounted in one end thereof and providing a housing for the magnet, cup-like member, coil and rod member, the cup member being adjustably mounted in said shell for ready regulation of the distance between the rod member and the diaphragm member; and a member of high magnetic premeability mounted in the other end of the shell and abutting the otherpole of the magnet, whereby substantially all of the magnetic flux between the poles is concentrated in a path through all of said members and the space between the diaphragm and rod members.

6. A pick-up of the character described for translating detonation pressure variations into corresponding electrical variations, including: a permanent magnet comprising a cylindrical slug; a cup-like member of non-magnetic material snugly receiving said magnet, this member having an opening in the bottom thereof; a coil; a rod member of high magnetic permeability extending through said coil and opening and having one end abutting one pole of said magnet with the rod member being of smaller diameter than said magnet; a flexible diaphragm member of high magnetic permeability, the plane 0f this member being transverse to the axis of the rod member and the center of the diaphragm being adjacent but slightly spaced from the other end of the red member; a substantially eylihelrieel shell of high magnetic permeability having the diaphragm member mounted in one end thereof and pro viding e housing for the magnet, cup-like member, coil and rod member, the cup member being ed= justably mounted in said shell for ready regula e tlon of the distance between the rod member and the dlephreem member, said apparatus being ptovitled with means including set screws 2301" W maintaining the rod and diaphragm members at the regulated, distance; and a member of high magnetic premeability mounted in the other end oi the shell and abutting the other pole of the magnet, whereby substantially all of the maghetlc flux between the poles is concentrated in e path through all of said members and the space between the diaphragm and rod. members.

BEN R. HIM-AER.

DAVIE) L. 

